1. Field of the Invention
The present invention relates to an electric heater (or else an auxiliary heater) for heating fluids in vehicles.
2. Discussion of the Background
Heaters, in particular heating, systems of this species, are required in vehicles, especially in cars, for various applications, such as for heating (warming up) the ambient air in the passenger compartment, for preheating the cooling water of water-cooled engines, for pre-glowing the spark plugs in self-igniting internal combustion engines, for heating fuel (diesel fuel) etc.
Heating systems of this type usually comprise a heating having at least one heating stage each including at least one heating element (for instance in the form of a heat resistor) for generating a particular heating capacity as well as a control unit for monitoring and/or controlling the time course and for presetting the heating capacity.
Especially in modern vehicles using high electric voltages in their electrical system, such as electrically operated vehicles, hybrid vehicles or fuel cell vehicles, fluid circulation systems must be heated due to missing or only temporarily available heat sources such as an internal combustion engine. These are usually water circulation systems that serve for heating the interior of the passenger compartment of a vehicle or for heating driving components such as the battery.
Since the engine waste heat is not or only temporarily available as a heat supply in these vehicles (or, respectively, discharges heat only to a restricted extent, as in the case of hybrid vehicles, for example), additional heating systems must be provided. For this purpose, especially electric heating systems are an option, as they are known from the state of the art, for instance according to DE 19 642 442 A1.
This known system must be adapted, however, when employed in modern vehicles especially having alternative drives, to the use of the high electrical system voltage common in those vehicles (maximum 500 volt). The system must in addition be electrically safe, i.e. it should have a high breakdown voltage, for example. Moreover the system should be controllable, thus absolutely requiring the use of electronics. Furthermore high mechanical stability is necessary, as during operation such system is exposed to a high vibration load and should remain safe also in the case of crash. What is decisive in this context is that a voltage transmission to the car body endangering the vehicle occupants is avoided in each common and extraordinary operating state.
It is basically known in the state of the art, especially in a car, to build in a cooling water heater. Among other things, also so called fuel heaters are offered which burn fuels and transmit the heat in a heat exchanger to the cooling water. At the end of the 90 s, however, electric cooling water heaters as described among other things in the afore-mentioned state of the art became established. This system which is equipped already with a safety concept for avoiding voltage transmissions to the car body is adapted to the electrical system voltage of a conventional car, however, and therefore functions only with low voltage of e.g. 12 V or 24 V, Moreover, from the state of the art a tubular heating unit (RHK) is known as electric heating element which is designed to be adjusted to a final voltage of 230 V (or 400 V). Those tubular heating units are not prepared to being used in a vehicle and especially in a car, however.